CN100496821C - Preparation of metal silver powder by direct hydrogen reduction of silver sulfate in alkali water slurry - Google Patents

Abstract

The invention proposes a new method for preparing metal silver powder through direct hydrogen reduction of silver sulfide in alkaline water slurry. Its main feature is that an appropriate amount of alkali is added to the water slurry to adjust the pH value to about 12. At the same time, a catalyst PdCl ₂ and a reducing agent ZnO are added to neutralize the S ^2- produced during the reduction process with ZnO, and combine to form ZnS to make the reduction reaction able to go on and on. By controlling the reduction temperature, hydrogen partial pressure and stirring speed, the reduction rate of silver in silver sulfide can reach more than 95%.

Description

Preparation of Silver Metal Powder by Direct Hydrogen Reduction of Silver Sulfide in Alkaline Water Slurry

technical field

The invention belongs to the field of metal powder preparation and provides a new method for preparing silver sulfide (Ag ₂ S) by direct hydrogen reduction after slurrying silver sulfide with water.

Background technique

Most non-ferrous metal mineral resources exist in nature in the form of sulfides. So far, the method of extracting metals from these metal sulfides is still dominated by pyrometallurgy. The sulfur dioxide produced during the smelting process will cause serious harm to the environment. . Therefore, people have been paying great attention to hydrometallurgy technology and have made great progress. For example, the full hydrometallurgical Shreeitt Gordon process of pressurized ammonia leaching-hydrogen reduction represented by the treatment of nickel and cobalt sulfide ores has been industrially applied in some countries such as the United States and Canada since the 1960s. The mine's pressurized hydrometallurgical process has also been industrialized. These hydrometallurgical processes usually include firstly leaching valuable metals in sulfide minerals into solution with ammonia or acid, followed by extraction and separation, and finally recovery of various metal products by reduction or electrowinning processes. Obviously, the process flow is relatively long and there are many processes. Therefore, people continue to explore new hydrometallurgical methods that can directly process metal sulfides.

Silver sulfide mainly exists in the form of argentite (Ag ₂ S) in nature. So far, there is no separate process for processing silver sulfide ore. It is usually smelted together with other non-ferrous metal sulfide ores (such as copper, nickel, lead, etc.). Silver is then enriched in the anode slime during the electrolytic refining of these crude metals, from which metallic silver is finally recovered. The overall process is long and the recovery rate of silver is relatively low.

Contents of the invention

The purpose of the present invention is to propose a new method of hydrometallurgy to directly process silver sulfide to prepare metallic silver powder, that is, silver sulfide (Ag ₂ S) is firstly made into a slurry by adding water and an appropriate amount of alkali, and then directly reducing it with hydrogen in an autoclave The metal silver powder is prepared, thereby eliminating the sulfur dioxide pollution produced during pyrometallurgy of nonferrous metal sulfide ores, and providing a new way for the direct treatment of silver sulfide ores.

In order to achieve this purpose, the alkaline water slurry system of silver sulfide is used, and hydrogenation is carried out directly in the autoclave for reduction. The Ag ₂ S concentration in the water slurry is 50g/l in terms of Ag, and the amount of alkali added is based on adjusting pH=10-12 in the water slurry system. ZnO should be added in an amount not greater than 10% of the stoichiometric amount to neutralize the S ^2- generated during the reduction process. At the same time, the catalyst PdCl ₂ is added, and its dosage is 0.1-0.25% of the Ag ₂ S amount. Under the conditions of reduction temperature 180-220°C, hydrogen partial pressure 2.0-3.0Mpa, and stirring speed 600-800 r/min, carry out hydrogenation reduction for 2-5 hours, and the reduction rate of silver in Ag ₂ S can reach more than 95%. After the reaction, through liquid-solid separation, washing, and drying at 50°C, the resulting product is a mixture of metallic silver, ZnS and a small amount of residual ZnO. Utilizing the difference between their specific gravity (the specific gravity of Ag is 10.5, the specific gravity of Ag ₂ S 7.3, the specific gravity of ZnO is 5.4, and the specific gravity of ZnO is 4.0) to separate to obtain the metal silver powder product.

Detailed ways

Example 1

8.0gAg ₂ S, 2.8gZnO, 3.0gNaOH, 1000mlH ₂ O and 20mg PdCl ₂ are slurried, placed in an autoclave, and reduced for 4 hours at 220°C and 2.6MPa hydrogen partial pressure, and Ag ₂ S is reduced to metallic silver The reduction rate is 98%.

Example 2

8.0g Ag ₂ S, 2.8g ZnO, 3.0g NaOH, 1000ml H ₂ O and 10mg PdCl ₂ are slurried, placed in an autoclave, and reduced for 4 hours at 220°C and 2.6MPa hydrogen partial pressure, Ag ₂ S reduced The reduction rate of metallic silver is 95%.

Claims (5)

1. silver sulfide direct hydrogen reduction in alkaline water slurry prepares the method for silver powder, it is characterized in that: silver sulfide adds water and an amount of alkali is made water slurry, the pH that described alkali is used for adjusting water slurry between 10～12, in water slurry, add an amount of reduction auxiliary agent ZnO so as in and the S that produces of reduction process ^2-, in conjunction with generating ZnS, simultaneously, in water slurry, add catalyst P dCl ₂, its consumption is 0.1～0.25% of a silver sulfide weight; Under 180～220 ℃ of reaction temperatures, hydrogen dividing potential drop 2.0～3.0MPa, stirring condition, carry out reductase 12～5h, prepare silver powder with hydrogen.

2. method according to claim 1 is characterized in that: the silver sulfide concentration in the described water slurry is counted 50g/l with Ag.

3. method according to claim 1 and 2 is characterized in that: described alkali is NaOH or potassium hydroxide.

4. method according to claim 1 and 2 is characterized in that: the speed of stirring is 600～800 rev/mins.

5. method according to claim 2 is characterized in that: the percent reduction of silver can reach more than 95% in the silver sulfide.